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Ground floor porch/first floor extension

Discussion in 'Building' started by cdbe, 21 Sep 2021.

  1. cdbe

    cdbe

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    I'm just starting on the above. It's actually a corner infill at the front of our house.

    The first floor will be knocked through to the existing (bathroom) to form a new bedroom - no problems with that.

    The ground floor will be a porch (existing house external door will be retained as well as new porch door on front). As you can see, it's quite narrow so I'm trying to maximize the width by removing the outer skin of the existing (RH, where the down pipe is) external wall. This will gain me 170mm (110 brick and 60mm cavity) but I presume I'll need to insulate it - but I don't know? The porch itself will be built to current "extension" thermal standards but will not be heated.

    I need to get it passed by building control, I don't want to be heating the porch from the adjacent lounge and I'll have to finish what will be the new single skinned internal wall so thought a layer of 50mm insulated plasterboard dabbed on as a minimum but will this satisfy regulations?

    Also, joining my new left hand wall to the existing, I normally cut out and continue the cavity but can't do here or the door will fall off, is dpc run up behind the wall starters acceptable?

    Thanks.

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  3. wessex101

    wessex101

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    I would say that as long as the external envelope (external walls and doors/windows) of the porch are built to the required U value standard then there is no need to insulate the internal wall between the porch and lounge. Technically as it is unheated a very pedantic building inspector may ask for insulation to the internal wall but remember a cupboard under the stairs or a larder is unheated and you don't need to insulate the internal walls separating them from the heated parts of the house. If it was a larger space like a garage it would be a different matter.

    Running some DPC up behind the wall starter will not prevent damp tracking horizontally across the existing external skin of brickwork towards the door jamb. For the sake of just 1 brick I think I'd bite the bullet and put in a vertical cut and then rebuild the outer brickwork leaf of the pier as a separate internal wall bonded in with the new internal leaf of the porch and discontinuous from the external leaf.
     
  4. cdbe

    cdbe

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    Thanks. Never really been sure about DPC up wall, seems to be something people do, out with the cutter it is!

    I had a look inside, expecting to find a return on the inner skin but there wasn't, so instead of being like the first sketch it was like the second, when I join the two inner skins I'll have to build a small nib in to pick up the door.

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